1. Technical Field
The present invention relates to a compound for organic light-emitting devices, and an organic light-emitting device including the compound.
2. Description of the Related Art
Organic light-emitting devices (OLEDs) are self-emitting devices having wide viewing angles, good contrast, quick response speeds, high brightness, and good driving voltage characteristics. Also, OLEDs can provide multicolored images.
A typical OLED has a structure including a substrate, and an anode, a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and a cathode sequentially stacked on the substrate. In this regard, the HTL, the EML, and the ETL are organic thin films formed of organic compounds.
An operating principle of an OLED having the above-described structure is as follows.
When a voltage is applied between the anode and the cathode, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. The holes and electrons recombine in the EML to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted.
A major factor affecting luminescent efficiency of an OLED is the luminescent material. Although fluorescent materials have been widely used as the luminescent material, development of a phosphorescent material capable of improving luminescent efficiency up to four times based on theoretical electroluminescence mechanisms would be an effective method for improving luminescent efficiency.
Currently, 4,4′-bis(carbazol-9-yl)biphenyl (CBP) is a known phosphorescent host material. High-efficiency organic light-emitting devices with hole blocking layers formed from 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or BAlq, and high-performance OLEDs using a BAlq derivative as a host are also known.
Although they have advantageous light-emitting characteristics, these existing luminescent materials have low glass transition temperatures and poor thermal stability, and thus may deteriorate during high-temperature deposition processes conducted under vacuum. The power efficiency of an OLED may be represented as: Power efficiency=(π/Voltage)×Current Efficiency. That is, the power efficiency is inversely proportional to voltage, and the power efficiency of the OLED should be high in order to reduce power consumption. In practice, OLEDs using common phosphorescent (host) materials, such as BAlq or CBP, may have higher driving voltages, but considerably higher current efficiency (cd/A), as compared with OLEDs using fluorescent materials, and thus are not advantageous in terms of power efficiency (Im/w). OLEDs using such existing host materials are also not satisfactory in terms of lifetime.